The cost of digital data processing circuitry has fallen spectacularly since computers began to be mass produced and this cost reduction has exerted a corresponding downward pressure on the cost of peripherals such as keyboards.
A conventional typewriter-type keyboard has moving keys controlling individual switches, but is relatively expensive to make. A membrane keyboard such as has been fitted to the Sinclair 2X 81 microcomputer enables substantial cost reductions to be made but provides no tactile feedback to the user as to whether depression of a key has provided a registrable signal. In other low cost computers such as that fitted to the Sinclair Spectrum the keys are formed integrally with a moulded rubber membrane. But the rubber sheet has to be overlaid by an apertured cover plate or bezel and the keys are used to close contacts in a membrane-type grid supported by a backing plate which is still relatively complex. Keyboards using silicone rubber sheets bearing conductive pads resiliently supported in contact elements formed in the sheets that directly close circuits between conductors on an underlying circuit board are sold by Maag Technic AG and provide a snap action and hence a degree of user tactile feedback. But again the silicone sheet is concealed within the keyboard structure and is intended to be used with separate typewriter- or calculator-style keys working in a bezel.